I just had this happen to me today. it was running android 8.1 and it just turned off and now won't boot. I had this unit in the NAS case and sparks were flying when I plugged it in as well.
Now the power light just blinks really fast and it won't turn on.

I agree with @lybin, it's not a scorch mark. I just checked my board (working normally) and it looks the same. Plus that part appears to be made of plastic, not metal, so this mark seems to be normal as both @lybin and I are seeing this on working boards.

Now the sparks on the other hand, that definitely sounds bad! This happened when you plugged in the power cable? @Firesped reporting this as well? This doesn't sound good. Sounds like something shorted out, or maybe there was some static electricity built up that could have contributed? Also, the LAN lights no longer lighting up corroborate the idea that something catastrophic happened.

We are talking about fully exposed circuit boards here so there are a lot of environmental factors at play. I'm sure almost none of us do it but it is recommended to take measures to avoid static buildup, like grounding/ static resistant gloves, etc. Can I ask, are you using the power supply sold by Pine64 to go with this board or some other power supply?